A plain journal bearing assembly, as defined in International Standard 4378/1-1983, has a plain bearing liner or insert which is formed as a cylindrical sleeve, typically of two identical halves and normally having cylindrical and coaxial inner and outer surfaces and axially oppositely directed end faces. This liner is received radially between a bearing housing having an inside surface against which lies the outer surface of the journal and a movable part having an outside surface or journal against which lies the inner surface of the liner. The liner is clamped so that it is substantially nonmovable on the housing part and so that substantially all of the relative sliding movement in the bearing takes place at the normally cylindrical interface between the inner liner surface and the journal. A classic use of such a plain journal bearing assembly is between a journal formed on a crankshaft and a connecting rod leading to a piston of an internal combustion engine, in which case the crankshaft is the movable inside part and the housing is formed by the connecting rod and all relative movement is angular.
The fit of the outer liner surface and the inside housing surface is invariably very tight so that the liner is held as solidly as possible. On the other hand at least microscopic play is always left between the inner liner surface and the journal so that same can move angularly and/or axially in the liner while being prevented from moving radially relative to the liner or housing.
It is possible to lubricate the inner liner surface in order to facilitate sliding although not strictly necessary to do so, so that some of the liquid lubricant can work its way into the contact area between the outer liner surface and the inside housing surface. Even in a normally unlubricated bearing, lubricants from other parts or other liquids and even solids frequently get into the liner/housing contact area.
The reason such deposits can get into this contact area is that, no matter how tightly the liner is secured in the housing and no matter how good the liner/housing fit is, so-called micromovements cannot be eliminated. Such movements can be caused by the tiny differences in coefficients of thermal expansion between the invariably different materials constituting the housing and liner, and from the inevitable tiny elastic deformation of the liner during use.
In U.S. Pat. No. 4,383,719 of Matzelle a solution to this buildup between the normally nonmoving contact area between a liner and a housing is proposed. The outer surface of the liner is made barrel-shaped, that is like a truncated ellipsoid. The result is that the micromovements squeeze any lubricant that gets into the housing/liner contact area outward, thereby keeping this contact area fairly clean. Unfortunately this squeezing action is not effective for hardened or caked on material. In addition machining the requires surface into the liner is somewhat complex and expensive.
As a result the standard solution to this problem has always been simply to fix the liner as solidly as possible in the housing. This can be done by the use of massive clamping rings and by making the liner as massive as possible. Either solution substantially increases the bulk and weight of the bearing assembly and therefore is not suitable for today's lightweight construction.